1. Field of the Invention
The invention relates to a method for making a field emission lamp.
2. Discussion of Related Art
Electrical lamps for daily living usually include incandescent lamps and fluorescent lamps. Since Thomas Edison invented the first viable incandescent lamps in 1879, the incandescent lamps have a long history for simple fabrication thereof. However, an incandescent lamp emits light by the heating of a tungsten filament and most of the electric energy used to power the lamp is converted into heat and thereby wasted. Therefore, a main shortcoming of the incandescent lamp is the low energy efficiency. Thus, the fluorescent lamps are widely used.
A typical conventional fluorescent lamp generally includes a transparent glass tube. The transparent glass tube has a white or colored fluorescent material coated on an inner surface thereof and a certain amount of mercury vapor filled therein. In use, electrons are accelerated by an electric field and the accelerated electrons collide with the mercury vapor. This collision causes excitation of the mercury vapor and this excitation causes radiation of ultraviolet rays. The ultraviolet rays are absorbed by the fluorescent material and the fluorescent material emits visible light. Compared with the incandescent lamps, the fluorescent lamps have relatively high electrical energy utilization ratios. However, when the glass tube is broken, the mercury vapor is prone to leak out therefrom, and thus, is poisonous and noxious to humans and is environmentally unsafe.
To address the above problems, a kind of fluorescent lamp (i.e., field emission lamp) without mercury vapor has been developed, as can be referenced in an article entitled “A Full Sealed Luminescent Tube Based on Carbon Nanotube Field Emission” and authored by Mirko Croci et al (page 329-336, Vol. 35, Microelectronics Journal 2004). A conventional cold cathode field emission lamp generally includes a transparent glass tube, a cathode, an anode, and glass feedthroughs. The glass feedthroughs are disposed on the ends of the glass tube. The cathode includes a cathode emitter and an electron emission layer formed thereon, and the anode includes a transparent conductive film and a phosphor layer. The transparent conductive film is formed on an inner surface of the glass tube and the phosphor layer is formed on the transparent conductive film facing the electron emission layer. In use, a strong electrical field is provided to excite the cathode emitters. A certain amount of electrons are emitted from the cathode emitters and then accelerated towards and collides with the fluorescent layer of the anode, thereby producing visible light.
The field emission lamp does not adopt mercury vapor, and is safe for humans and environmentally friendly. Furthermore, the field emission lamp adopts a cold cathode, thereby providing a high electrical energy utilization ratio and low energy consumption.
Conventionally, the fabrication of the field emission lamp includes the process of fabricating the cathode emitters, forming the anode, and encapsulating the glass tube. The encapsulation procedure includes connecting the glass feedthroughs with the ends of the glass tube to seal the glass tube. Currently, a colloid is used to connect the glass feedthroughs to the glass tube. However, this sealing method has a poor encapsulation effect and thus affects the performance life of the field emission lamp. Moreover, this method is complicated and time-consuming and not suitable for mass production of the field emission lamp. And thus the field emission lamp has a relatively high cost.
What is needed, therefore, is a method for making a field emission lamp that overcomes the above-mentioned shortcomings, ensuring a high degree of vacuum in the field emission lamp, thus providing a better field emission performance during the use thereof.